import math
AB = eval(input())
CD = eval(input())
AD = AB/2
OA = (AD*AD+CD*CD)/(2*CD)
AOB=2*math.asin(AD/OA)
sec = (AOB/(2*3.1415926))*3.1415926*(OA*OA)
tr = 0.5*OA*OA*math.sin(AOB)
arc = sec - tr
print(f'{arc:.2f}')